In marking techniques, for certain applications such as when supports are dark-colored, it is necessary to use inks with large amounts of pigments, such as titanium oxide particles, which make the ink opaque and white.
Using such an ink in standard machines causes several problems. We know that in an ink jet printing device using a continuous jet of ink drops, the drops must be led pressurized to an assembly called the modulation body, with a projection nozzle at its tip. Also, the ink drops not used for printing must be gathered and returned to the recovery reservoir to circulate again in the printing device. Printing quality of a printer of this type is closely related to the speed of ejection of the ink through the nozzle. This speed can be altered by varying the pressure upstream from the opening, as well as by a change in ink viscosity, which may be due to a loss by evaporation of the ink solvent which is often volatile.
As regards ink pressurization devices and those for recovering unused ink drops, it is common to see pumps implemented in a first type of machine. This is true of the ink circuit described in French patent no. 2,353,441 registered by the Applicant. In application with inks that are heavy in pigments, the disadvantage is that these pigments quickly alter the pumps, reducing their reliability. Moreover, pumps create cyclic variations in pressure that can harm printing quality.
There are devices that use pressurized gas reservoirs. This technique requires the use of buffer reservoirs to recover the ink drops in the transfer phase from recovery reservoir to main reservoir. An example of this is the ink circuit described in French patent no. 2,405,819. Having several of these reservoirs does not easily lend itself to circulating a pigment ink, since the pigment tends to be deposited by gravity at the bottom of the reservoirs. Finally, implementing pressurized gas reservoirs, usually of compressed air, also requires a second energy source for the machines using them.